Small Cu2CoSnS4(CCTS) nanocrystals were synthesized via a facile solvothermal method in large quantity. The morphology, size, structure and composition of the as-synthesized CCTS were char-acterized by XRD, TEM, and UV-Visible absorption spectra. The results showed that the products were nanocrystals with average particle size of 13.2 nm, uniform size and good dispersibility. T1weighted MR images of CCTS solutions were acquired on a 3.0-T clinical MR scanner, revealing the obvious concentration-dependent brightening effect. Importantly, the r1 value increased dramatically from the initial value to 7.64 mM−1S−1. Remarkable brightening effect in the tumor of injected mice was observed. These results demonstrate that the CCTS nanocrystals could be the promising MRI theranostic nano-agents and have a great application prospect.